1. Field of the Invention
The present invention relates to a continuous casting immersion nozzle for pouring molten steel from a tundish into a mold and particularly to an immersion nozzle used for high-speed casting of thin to medium thick slabs.
2. Description of the Related Art
In continuous casting operation, appropriate control (e.g., prevention of drifts, suppression of level fluctuation in the mold, and the like) of a flow of molten steel in a mold is important to ensure and maintain quality of casting steel products as well as to carry out the operation safely and smoothly. Especially in high-speed casting of thin to medium thick slabs (about 50 mm to 150 mm in thickness), a width-thickness ratio (slab width/slab thickness) thereof is greater than that of normal slabs, and therefore it is often difficult to adjust the flow of the molten steel in the mold appropriately.
To achieve appropriate control of a flow of molten steel in a mold, the present inventors developed (invented) a continuous casting immersion nozzle as disclosed in Japanese Unexamined Patent Application Publication No. 2009-233717, for example. The continuous casting immersion nozzle includes a tubular body having a passage, and at least at a lower section of the tubular body includes a flat cross section. The lower section includes two pairs of outlets, one is disposed in narrow sidewalls thereof and the other is disposed in a bottom thereof. And, provided between the outlets disposed in the narrow sidewalls are ridges projecting inward from wide inner walls of the passage. In this way, a maximum flow velocity of the molten steel flow that collides with the narrow sidewalls of the mold is reduced, and thus a velocity of a reverse flow can be reduced. As a result, drifts and level fluctuation of the molten steel flow in the mold can be reduced, improving slab quality and productivity.
To improve a flow (movement) of molten steel discharged into a mold, International Publication No. WO1998/014292 discloses a casting nozzle including an inlet disposed at an upper end of a tubular body, a pair of upper outlets and a pair of lower outlets disposed at a lower end of the tubular body, and a baffle for dividing the molten steel flow into an outer stream discharged through the upper outlets and a central stream discharged through the lower outlets.